1. Field of the Invention
The present invention relates to an electromagnetic drive and a flow controller using the same.
2. Description of the Related Art
Generally, electromagnetic drives are known in which a mover and a stator form a magnetic circuit, and the mover is driven to reciprocate. A kind of these electromagnetic drives is one in which the mover is supported directly by the inner periphery of an accommodating portion of the stator. The mover is attracted in one of its reciprocating directions by a magnetic attractive force that acts between an attracting portion of the stator and the mover (for example, see Japanese Patent Laid-Open Publication No. 2002-222710, hereinafter, patent document 1).
In the electromagnetic drive disclosed in the foregoing patent document 1, the outer periphery of them over is plated with nickel phosphide to achieve higher hardness levels, which reduces the sliding resistance that occurs between the mover and the accommodating portion. Nevertheless, the mover and the accommodating portion undergo a radial magneto motive force between them, which is called a side force. This side force brings the mover and the accommodating portion into tight contact and hampers sufficient reduction of the sliding resistance. Since the side force increases in proportion to the current supplied to the coil, the reciprocating position of the mover under the sliding resistance ascribable to the side force is not proportional to the current supplied to the coil, and thus the position is difficult to control.